Can you help and explain this to me, please

X=20
All straight angles are 180 degrees so we’re gonna set up an equation that adds up to 180: x+100+3x=180.
First subtract 100 from both sides and combine the x and 3x to get 4x=80.
Divide both sides by 4 to get x alone and the final answer of x=20.

Larry wants to deposit $350 as a principle amount, with an interest of 4% compoundedquarterly.
=> 350 * 0.04 = 14 dollars per quarter.
=> 14 * 4 quarter per year = 56 dollars per year
=> 56 * 2 = 112 dollars for 2 years

Peggy wants to deposit $350 as the principle amount, with an interest of 6% compounded monthly. 
=> 350 * 0.06 = 21 dollars per month
=> 21 dollars * 24 months = 504 dollars in 2 years.